U.S. patent number 6,430,398 [Application Number 09/332,942] was granted by the patent office on 2002-08-06 for method for improving performance of a mobile radiocommunication system using power control.
This patent grant is currently assigned to Alcatel. Invention is credited to Patrick Blanc.
United States Patent |
6,430,398 |
Blanc |
August 6, 2002 |
Method for improving performance of a mobile radiocommunication
system using power control
Abstract
A method for improving performances of a mobile
radiocommunication system using a power control loop which controls
power according to a transmission quality target value, and an
adjustment process for adjusting said transmission quality target
value, a method wherein said adjustment process is controlled based
on an assessment of the convergence of said power control loop
around said transmission quality target value.
Inventors: |
Blanc; Patrick (Issy les
Moulineaux, FR) |
Assignee: |
Alcatel (Paris,
FR)
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Family
ID: |
8241980 |
Appl.
No.: |
09/332,942 |
Filed: |
June 15, 1999 |
Foreign Application Priority Data
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May 21, 1999 [EP] |
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99401231 |
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Current U.S.
Class: |
455/67.13;
455/522; 455/69 |
Current CPC
Class: |
H04W
52/12 (20130101); H04W 52/20 (20130101); H04W
52/225 (20130101); H04W 52/24 (20130101) |
Current International
Class: |
H04B
7/005 (20060101); H04Q 007/20 () |
Field of
Search: |
;455/63,67.1,69,522,67.3
;370/332,333,335 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 709 973 |
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May 1996 |
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EP |
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0 856 955 |
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Aug 1998 |
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EP |
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Other References
Yates R D et al: "Soft Dropping Power Control" IEEE Vehicular
Technology Conference, US, New York, IEEE, vol. Conf. 47, pp.
1694-1698 XP000738652 ISBN: 0-7803-3660-7..
|
Primary Examiner: Maung; Nay
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A method for improving performances of a mobile
radiocommunication system using a power control loop which controls
power according to a transmission quality target value, and an
adjustment process for adjusting said transmission quality target
value, a method wherein said adjustment process is controlled based
on an assessment of the convergence of said power control loop
around said transmission quality target value.
2. A method according to claim 1, wherein said control of said
adjustment process includes not performing any adjustment, if said
power control loop has not converged around said transmission
quality target value.
3. A method according to claim 1, wherein said transmission quality
is represented by a Signal-to-Interference Ratio .
4. A method according to claim 1, wherein said adjustment process
is an outer loop which adjusts a quality of service around a
quality of service target value.
5. A method according to claim 1, wherein said mobile
radiocommunication system is of CDMA type.
6. A method according to claim 1, wherein said power control is
performed in an uplink transmission direction of said mobile
radiocommunication system, using an uplink power control loop and
an uplink adjustment process, and wherein said uplink adjustment
process is controlled, based on an assessement of the convergence
of said uplink power control loop.
7. A mobile radiocommunication network for performing a method
according to claim 6, said mobile radiocommunication network
comprising means for performing said uplink power control loop,
means for performing said uplink adjustment process, and means for
controlling said uplink adjustment process based on an assessment
of the convergence of said uplink power control loop.
8. A mobile radiocommunication network according to claims 7, said
mobile radiocommunication network being of the type comprising at
least one base station, comprising means for performing said uplink
power control loop, and at least one base station controller,
comprising means for performing said uplink adjustment process.
9. A base station of a mobile radiocommunication network according
to claim 8, comprising: means for performing measurements necessary
for the assessment of the convergence of said uplink power control
loop, means for sending such measurements to a base station
controller.
10. A base station controller of a mobile radiocommunication
network according to claim 8, comprising: means for receiving
measurements necessary for the assessment of the convergence of
said uplink power control loop, from a base station, means for
assessing the convergence of said uplink power control loop, based
on such measurements, and for controlling said uplink adjustment
process, based on this assessment.
11. A method according to claim 1, wherein said power control is
performed in a downlink transmission direction of said mobile
radiocommunication system, using a downlink power control loop and
a downlink adjustment process, and wherein said downlink adjustment
process is controlled, based on an assessement of the convergence
of said downlink power control loop.
12. A mobile station for performing a method according to claim 11,
said mobile station comprising means for performing said downlink
power control loop, means for performing said downlink adjustment
process, and means for controlling said downlink adjustment process
based on an assessment of the convergence of said downlink power
control loop.
13. A mobile station according to claim 12, comprising: means for
performing measurements necessary for the assessment of the
convergence of said downlink power control loop, means for
assessing the convergence of said downlink power control loop,
based on such measurements, and for controlling said downlink
adjustment process, based on this assessment.
14. A mobile station according to claim 13, further comprising
means for receiving parameters required for said assessment of
convergence of said downlink power control loop, from a mobile
radiocommunication network.
15. A mobile radiocommunication system including at least one
mobile station according to claim 12.
16. A method for improving performances of a mobile
radiocommunication system using a power control loop which controls
power according to a transmission quality target value, and an
adjustment process for adjusting said transmission quality target
value, a method wherein said adjustment process is controlled based
on an assessment of the convergence of said power control loop
around said transmission quality target value, wherein convergence
of said power control loop is assessed by determining if the
difference between an estimated average transmission quality and
said transmission quality target value is within given margins.
17. A method according to claim 16, wherein said margins are
determined so as to take into account power control errors.
18. A method according to claim 16, wherein said margins are
optimised according to radio conditions.
19. A method according to claim 16, wherein said margins are
different depending on whether said adjustment requires increasing
or reducing said transmission quality target value.
20. A method according to claim 16, wherein said estimated average
transmission transmission quality is estimated on an averaging
period which is long enough to enable said power control loop to
converge, but not too long to take into account fast changes in
power control requirements.
21. A method according to claim 16, wherein said averaging period
is optimised according to radio conditions.
22. A method for improving performances of a mobile
radiocommunication system using a power control loop which controls
power according to a transmission quality target value, and an
adjustment process for adjusting said transmission quality target
value, a method wherein said adjustment process is controlled based
on an assessment of the convergence of said power control loop
around said transmission quality target value, wherein convergence
of said power control loop is assessed by determining if, among
successive values representative of an estimated average
transmission quality, at least one of these values is above said
transmission quality target value and at least one of these values
is below said transmission quality target value.
23. A method for improving the performance of a mobile radio
communication system using a downlink power control loop for
controlling power according to a SIR target value, and a using a
downlink adjustment process for adjusting said SIR target value, a
method comprising: making a convergence assessment as to whether
said downlink power control loop is converging around said SIR
target value; and controlling said downlink adjustment process
based on said convergence assessment; wherein said SIR target value
is not increased by said downlink adjustment process when said
convergence assessment indicates that said downlink power control
loop is not converging around said SIR target value.
24. The method as set forth in claim 23, wherein said convergence
assessment is made by comparing an averaged, measured SIR to said
SIR target value.
25. A mobile station, comprising: means for performing a downlink
power control loop for controlling power according to a SIR target
value; means for performing a downlink adjustment process for
adjusting said SIR target value; and means for preventing, when
said downlink power control loop is not converging around said SIR
target value, said downlink adjustment process from increasing said
SIR target value.
26. The mobile station as set forth in claim 25, further comprising
means for assessing whether said downlink power control loop is or
is not converging around said SIR target value of said power
control loop by comparing an averaged, measured SIR to said SIR
target value.
27. A mobile radiocommunication system including at least one
mobile station according to claim 25.
Description
BACKGROUND OF THE INVENTION
The present invention is generally concerned with mobile
radiocommunication systems.
The present invention is more particularly concerned with power
control used in such systems to improve performances (in terms of
quality of service, of capacity, . . . etc.).
The present invention is in particular applicable to mobile
radiocommunication systems of CDMA ("Code Division Multiple
Access") type. In particular, the present invention is applicable
to UMTS ("Universal Mobile Telecommunication System").
One type of power control which is used in CDMA systems is the
so-called closed-loop power control.
The closed loop generally runs on a fast basis in order to adjust
the transmission quality (generally represented by the SIR, or
"Signal-to-lnterference Ratio") around a transmission quality
target value (generally a SIR.sub.target value), by sending
appropriate power control commands back to the transmitter. The
closed loop thus sends an "up" power control command back to the
transmitter when the estimated SIR is below the SIR.sub.target
value, or a "down" power control command otherwise.
The SIR.sub.target value is generally adjusted by a so-called outer
loop. The outer loop generally runs on a slower basis in order to
adjust the quality of service (generally represented by the BER, or
"Bit Error Rate", or the FER, or "Frame Error Rate") around a
quality of service target value (generally a BER or FER target
value). The outer loop thus increases the SIR.sub.target value when
an estimated BER or FER is above a BER or FER target value, or
reduces it otherwise.
Such an implementation may lead to such situations where the
SIR.sub.target value is needlessly increased, therefore needlessly
increasing the interference level in the system.
This may in particular be the case under such conditions as when
the transmitter has already reached its maximum transmit power, or
when the system has become overloaded. In such a case the
SIR.sub.target value is uselessly increased, while this cannot
result in any quality improvement. This may not be considered as a
drawback in itself, as long as such conditions apply, but the
SIR.sub.target value may therefore reach a too high value, and,
when such conditions no longer apply, this will result in setting
the transmit power at a level higher than necessary, therefore
needlessly increasing the interference level in the system, until
the algorithm reaches a correct value again.
The outer loop is usually implemented at the receiver side, in
order to reduce adaptation delays between quality measurements and
SIR.sub.target setting However, the receiver may not have means to
know why the quality of service cannot be maintained with the
current SIR.sub.target value, and, as indicated above, may try to
increase it, even though the current SIR.sub.target value cannot be
reached due to network overload for instance.
Therefore there is a need to provide a power control method
avoiding such drawbacks.
SUMMARY OF THE INVENTION
An object of the present invention is therefore a method for
improving performances of a mobile radiocommunication system using
a power control loop which controls power according to a
transmission quality target value, and an adjustment process for
adjusting said transmission quality target value, a method wherein
said adjustment process is controlled based on an assessment of the
convergence of said power control loop around said transmission
quality target value.
According to another object of this invention, said control of said
adjustment process includes not performing any adjustment, if said
power control loop has not converged around said transmission
quality target value.
According to another object of this invention, convergence of said
power control loop is assessed by determining if a difference
between an estimated average transmission quality and said
transmission quality target value is within given margins.
According to another object of this invention, said margins are
determined so as to take into account power control errors.
According to another object of this invention, said margins are
optimised according to radio conditions.
According to another object of this invention, said margins are
different depending on whether said adjustment requires increasing
or reducing said transmission quality target value.
According to another object of this invention, said estimated
average transmission transmission quality is estimated on an
averaging period which is long enough to enable said power control
loop to converge, but not too long to take into account fast
changes in power control requirements.
According to another object of this invention, said averaging
period is optimised according to radio conditions.
According to another object of this invention, convergence of said
loop is assessed by determining if, among successive values
representative of an estimated average transmission quality, at
least one of these values is above said transmission quality target
value and at least one of these values is below said transmission
quality target value.
According to another object of this invention, said transmission
quality is represented by a Signal-to-Interference Ratio (SIR).
According to another object of this invention, said adjustment
process is an outer loop which adjusts a quality of service around
a quality of service target value.
According to another object of the invention, said mobile
radiocommunication system is of CDMA type.
According to another object of the invention, said power control is
performed in on uplink transmission direction of said mobile
radiocommunication system, using an uplink power control loop and
an uplink adjustment process, and said uplink adjustment process is
controlled, based on an assessement of the convergence of said
uplink power control loop.
According to another object of the invention, said power control is
performed in a downlink transmission direction of said mobile
radiocommunication system, using a downlink power control loop and
a downlink adjustment process, and said downlink adjustment process
is controlled, based on an assessement of the convergence of said
downlink power control loop.
The present invention also has for its object a mobile
radiocommunication network for performing such a method, said
mobile radiocommunication network comprising means for performing
said uplink power control loop, means for performing said uplink
adjustment process, and means for controlling said uplink
adjustment process, based on an assessment of the convergence of
said uplink power control loop.
According to another object of this invention, said mobile
radiocommunication network is of the type comprising at least one
base station, comprising means for performing said uplink power
control loop, and at least one base station controller, comprising
means for performing said uplink adjustment process.
According to another object of this invention, a base station of
such a network comprises; means for performing measurements
necessary for the assessment of the convergence of said uplink
power control loop, means for sending such measurements to a base
station controller.
According to another object of this invention, a base station
controller of such a network comprises: means for receiving such
measurements from a base station, means for assessing the
convergence of said uplink power control loop, based on such
measurements , and for controlling said uplink adjustment process,
based on this assessment.
The present invention also has for its object a mobile station for
performing such a method, said mobile station comprising means for
performing said downlink power control loop, means for performing
said downlink adjustment process, and means for controlling said
downlink adjustment process, based on an assessment of the
convergence of said downlink power control loop.
According to another object of this invention, such a mobile
station comprises: means for performing measurements necessary for
the assessment of the convergence of said downlink power control
loop, means for assessing the convergence of said downlink power
control loop, based on such measurements, and for controlling said
downlink adjustment process, based on this assessment.
According to another object of this invention, such a mobile
station further comprises means for receiving parameters required
for said assessment of convergence of said downlink power control
loop, from a mobile radiocommunication network.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects of the present invention will become more
apparent from the following description taken in conjunction with
the accompanying drawings:
FIG. 1 is a diagram intended to illustrate a method according to
the invention,
FIG. 2 is a diagram intended to illustrate the general architecture
of the radio access network, or "UTRAN" ("UMTS Terrestrial Radio
Access Network"), of UMTS system,
FIG. 3 is a diagram intended to illustrate an example of means
which may be used in an entity like a base station or Node B of
UTRAN, and in an entity like a base station controller or SRNC of
UTRAN, to perform a method according to the present invention, for
uplink power control,
FIG. 4 is a diagram intended to illustrate an example of means
which may be used in a mobile station, or user equipment (UE) to
perform a method according to the present invention, for downlink
power control.
DETAILED DESCRIPTION OF THE INVENTION
The present invention thus has for its object a method for
improving performances of a mobile radiocommunication system using
a power control loop which controls power according to a
transmission quality target value, and an adjustment process for
adjusting said transmission quality target value, a method wherein
said adjustment process is controlled, based on an assessment of
the convergence of said power control loop around said transmission
quality target value.
Such a method may be illustrated by the diagram of FIG. 1, where: 1
refers to a power control loop, 2 refers to said adjustment process
3 refers to an assessment of the convergence of said power control
loop, 4 refers to a control of said adjustment process, based on
said assessment.
Generally, such a method enables to optimise performances, by
optimising the adjustment process.
In particular, by providing that no adjustment of the transmission
quality target value is performed if said power control loop has
not yet converged around this target value, this enables to avoid
the above mentioned drawbacks.
Still in particular, by considering the current case where the
adjustment process is the outer loop algorithm as mentioned above,
and the power control loop is the closed loop as mentioned above,
this may be expressed by the following algorithm: If outer loop
algorithm requests a change of SIR.sub.target, If closed loop power
control has converged, the request is accepted Else the request is
rejected.
An example of implementation of such an algorithm may be expressed
as follows: If (Avgd_FER<FER.sub.target) and
(.vertline.SIR.sub.av -SIR.sub.target.vertline.<.eta.),
SIR.sub.target =SIR.sub.target -SIR.sub.dec-step if
(Avgd_FER>FER.sub.target) and (.vertline.SIR.sub.av
-SIR.sub.target.vertline.<.epsilon.), SIR.sub.target
=SIR.sub.target -SIR.sub.inc--step
In this example SIR.sub.inc--step and SIR.sub.dec--step are the
specified steps for updating (increasing, respectively decreasing)
SIR.sub.target values.
In this example (Avgd_FER<FER.sub.target) or
(Avgd_FER>FER.sub.target) are the conditions in which the outer
loop requests updating SIR.sub.target where: Avgd_FER is a measured
FER averaged over a given period. Other quality parameters could be
used such as Block Error Rate, number of retransmissions of PDU in
RLC for packet services, etc. FER.sub.target is the FER target
value specified for the bearer service (given at call or session
set up).
In this example, convergence of the power control closed loop is
assessed by determining if the difference between an estimated
average transmission quality and said transmission quality target
value is within given margins, i.e. if
where: SIR.sub.target is the SIR target value set by the outer loop
algorithm and used by the closed loop power control SIR.sub.av is
the SIR measured and averaged over a given averaging period. This
averaging period is a parameter of the system that may be optimised
according to radio conditions. It should start of least after the
lost change in SIR.sub.target value, should be long enough to allow
the closed loop to reach the new value, but should not be too long
to identify fast changes in case of overload situations for
instance .epsilon.,.eta. are margins related to the difference
between SIR.sub.av measurements and SIR target values (for the case
where SIR.sub.target needs to be increased, respectively
decreased), taking into account power control errors These
parameters may also be optimised according to radio conditions.
Other examples may be envisaged to assess the convergence of the
closed loop power control. For instance, it may be considered that
the closed loop has converged, when among successive values of
SIR.sub.av at least one of these values is below SIR.sub.target and
at least one of these values is above SIR.sub.target.
Besides, it should be noted that parameters other than SIR might be
used to assess the convergence of the closed loop power control, to
take into account non precise measurements in case of bad SIR
estimation (for low SIR values in particular).
The present invention may be applied to uplink power control,
downlink power control, or both uplink and downlink power
control
As compared to known methods, the method according to the invention
may require additional measurements as well as additional
signalling to be performed.
As an example, an application of the present invention to the UTRAN
architecture of UMTS will be disclosed in the following.
As recalled in FIG. 2, the current UTRAN architecture comprises:
base stations, called "Node B", which communicate with mobile
stations or "User Equipments" (UE) via a radio interface called
"Uu", base station controllers, called "Radio Network Controllers"
or RNC, which communicate with Nodes B via an interface called
"lub" (each RNC controlling a plurality of Nodes B).
Within this architecture, for uplink power control the closed loop
is currently implemented in Node B. while the outer loop is
currently implemented in RNC; for downlink power control both loops
are currently implemented in UE.
A method according to the invention may then require additional
measurements to be performed, in Node B for uplink power control
and in UE for downlink power control, as well as additional
signalling to be performed between Node B and RNC at the interface
lub, for uplink power control.
As illustrated at FIG. 3, a Node B may therefore comprise, besides
other means which may be classical and which are not mentioned
here: means 10 for performing measurements required for the
assessment of convergence of the uplink power control loop, means
11 for sending such measurements to RNC.
As illustrated at FIG. 3, a RNC may therefore comprise, besides
other means which may be classical and which are not mentioned
here: means 13 for receiving such measurements from Node B, means
14 for assessing the convergence of said uplink power control loop,
based on such measurements, and for controlling the uplink
adjustment process, or uplink outer loop, based on this
assessment.
Means like 10, 11, 13, 14 work together so as to perform the above
disclosed method, for uplink power control. Such means do not need
to be more fully disclosed than by their above disclosed function,
for a person skilled in the art. Besides, the required signalling
may be performed according to known types of signalling procedures
in such types of systems, and therefore does not either require to
be more fully disclosed, for a person skilled in the art.
For example, the measurements required for the assessment of
convergence, and sent by Node B to RNC across the lub interface,
may be sent in bond with data PDU ("Packet Data Unit") or out of
band.
For example, such measurements as SIR.sub.av (such as SIR averaged
over the transmission time period of a data frame) may be sent in
bond for each uplink data frame.
As illustrated at FIG. 4, a User Equipment UE may comprise, besides
other means which may be classical and which are not mentioned
here: means 15 for performing measurements required for the
assessment of convergence of the downlink power control closed
loop, means 16 for assessing said convergence, based on such
measurements, and for controlling the downlink adjustment process,
or downlink outer loop, based on this assessment.
No additionnal signalling is therefore required for downlink power
control.
However, parameters necessary for the assessment of convergence,
such as for instance parameter e referred to in the above disclosed
example may need to be signalled to each UE, in case network
control on said downlink adjustment control would be needed.
Alternatively, parameter .epsilon.for instance may be evaluated by
the UE from past measurements.
Means like 15, 16 work together so as to perform the above
disclosed method, for downlink power control. Such means do not
either require to be more fully disclosed than by their above
disclosed function, for a person skilled in the art.
* * * * *